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Molecular analysis of lake-sediment organic matter: long-term dynamics and environmental implications in boreal lakes
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.ORCID-id: 0000-0001-9659-2722
2023 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)Alternativ titel
Molekylär analys av organiskt material i sjösediment : långtidsdynamik och miljöpåverkan i boreala sjöar. (Svenska)
Abstract [en]

Lake sediment organic matter is material composed of residues from plants, algae, animals, fungi and bacteria. Its molecular composition is dependent on the sources as well as secondary biotic and abiotic transformations, which combined generates a highly complex matrix. Considering that organic matter plays a key role in carbon and nitrogen cycle, and its composition affects many different biogeochemical reactions, paleolimnologic studies have payed proportionately little attention to the organic matter composition compared with the other sediment fractions, even though organic matter makes up 20–60 % of the dry sediment mass in boreal and subarctic lakes. This thesis therefore primarily aims to explore and evaluate two methods; pyrolysis-gas chromatography/mass spectrometry (Pyrolysis-GC/MS) and diffuse reflectance Fourier-transform infrared spectroscopy (DRIFTS) for characterisation of bulk organic matter at the molecular level, both which have been extensively used for soils and peat and which balances the need for cost and time-effective analysis and for analytical detail.

With pyrolysis-GC/MS the organic matter composition and long-term dynamics in two neighbouring boreal lakes is explored and compared with the conventional bulk carbon and nitrogen contents and their stable isotopes. Both pyrolysis data and conventional data capture the timing of organic matter compositional changes, but only pyrolysis provides detailed information on how the composition changes, which allows for a deeper understanding of the processes behind the changes. The same two lakes are also analysed with DRIFTS and with this approach information on the major organic compound groups aromatics, lignin, aliphatics, proteins and polysaccharides is extracted. In combination with the rapid analysis time and low cost, DRIFTS emerges as a very useful tool for rapid yet informative organic matter analysis. DRIFTS is then evaluated as a stand-alone tool for sediment characterisation in four mountain lakes. The four lakes all have different sediment composition and as a result of the multi-fraction information obtained with DRIFTS compositional differences can be related and explained in terms of their individual lake and landscape settings. The importance of landscape setting is further highlighted in the synthesis of the long-term dynamics of lake-water quality in seven lakes where development trajectories and responses to different types of disturbances are connected to the extent of peatlands within the lake catchments. This thesis demonstrates the advantages of two different approaches for more detailed lake sediment organic matter characterisation and advances our understanding of the molecular organic matter composition in boreal lakes over the Holocene, and how landscape setting affects both the organic matter composition and the sensitivity of lakes to disturbance.

Ort, förlag, år, upplaga, sidor
Umeå: Umeå University , 2023. , s. 23
Nyckelord [en]
Lake sediment, Holocene, organic matter, Pyrolysis-GC/MS, mid-infrared spectroscopy, boreal
Nationell ämneskategori
Miljövetenskap
Identifikatorer
URN: urn:nbn:se:umu:diva-213753ISBN: 978-91-8070-144-0 (tryckt)ISBN: 978-91-8070-145-7 (digital)OAI: oai:DiVA.org:umu-213753DiVA, id: diva2:1791969
Disputation
2023-09-22, NAT.D.450, Naturvetarhuset, Umeå Universitet, Umeå, 09:00 (Engelska)
Opponent
Handledare
Tillgänglig från: 2023-09-01 Skapad: 2023-08-28 Senast uppdaterad: 2023-08-28Bibliografiskt granskad
Delarbeten
1. Investigating molecular changes in organic matter composition in two Holocene lake-sediment records from central Sweden using pyrolysis-GC/MS
Öppna denna publikation i ny flik eller fönster >>Investigating molecular changes in organic matter composition in two Holocene lake-sediment records from central Sweden using pyrolysis-GC/MS
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2017 (Engelska)Ingår i: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 122, nr 6, s. 1423-1438Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Organic matter (OM) is a key component of lake sediments, affecting carbon, nutrient, and trace metal cycling at local and global scales. Yet little is known about long-term (millennial) changes in OM composition due to the inherent chemical complexity arising from multiple OM sources and from secondary transformations. In this study we explore how the molecular composition of OM changes throughout the Holocene in two adjacent boreal lakes in central Sweden and compare molecular-level information with conventional OM variables, including total carbon, total nitrogen, C:N ratios, delta C-13, and delta N-15. To characterize the molecular OM composition, we employed a new method based on pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), which yields semiquantitative data on > 100 organic compounds of different origin and degradation status. We identify large changes in OM composition after deglaciation (circa 8500 +/- 500 B.C.), associated with early landscape development, and during the most recent 4050 years, driven by degradation processes. With molecular(-)level information we can also distinguish between natural landscape development and human catchment disturbance during the last 1700 years. Our study demonstrates that characterization of the molecular OM composition by the high-throughput PyGC/MS method is an efficient complement to conventional OM variables for identification and understanding of past OM dynamics in lake-sediment records. Holocene changes observed for pyrolytic compounds and compound classes known for having different reactivity indicate the need for further paleo-reconstruction of the molecular OM composition to better understand both past and future OM dynamics and associated environmental changes.

Ort, förlag, år, upplaga, sidor
American Geophysical Union (AGU), 2017
Nationell ämneskategori
Multidisciplinär geovetenskap
Identifikatorer
urn:nbn:se:umu:diva-138425 (URN)10.1002/2016JG003715 (DOI)000406520900008 ()2-s2.0-85021698702 (Scopus ID)
Tillgänglig från: 2017-08-23 Skapad: 2017-08-23 Senast uppdaterad: 2023-08-28Bibliografiskt granskad
2. Application of mid-infrared spectroscopy for the quantitative and qualitative analysis of organic matter in Holocene sediment records
Öppna denna publikation i ny flik eller fönster >>Application of mid-infrared spectroscopy for the quantitative and qualitative analysis of organic matter in Holocene sediment records
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2024 (Engelska)Ingår i: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 34, nr 3, s. 259-273Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The organic matter composition of lake sediments influences important in-lake biogeochemical processes and stores information on environmental changes. Extracting this information is notoriously difficult because of the complexity of the organic matter matrix, which routinely imposes trade-offs between high temporal and analytical detail in the selection of methods of analysis. Here, we demonstrate the potential of diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) for achieving both of these objectives using untreated bulk samples from two Holocene lake-sediment cores from central Sweden. We develop quantitative models for sediment total organic carbon (TOC) with the same predictive abilities as models based on samples diluted with KBr and qualitatively characterize the organic matter using a spectra processing-pipeline combined with principal component analysis. In the qualitative analysis we identified four organic matter sub-fractions and the interpretation of these is supported and further advanced with molecular data from pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Within these organic fractions, compound groups such as aromatics, lignin, aliphatics, proteins and polysaccharides were identified by means of DRIFTS and the analyses and processes outlined here enables rapid and detailed quantitative and qualitative analysis of sediment organic matter. The DRIFTS approach can be used as stand-alone method for OM characterization with high temporal resolution in Holocene sediment records. It may also function as a screening process for more specific analyses of sample subsets, such as when coupled with pyrolysis-GC/MS to further tease apart the OM composition, identify sources and determine degradation status.

Ort, förlag, år, upplaga, sidor
Sage Publications, 2024
Nationell ämneskategori
Miljövetenskap
Identifikatorer
urn:nbn:se:umu:diva-213750 (URN)10.1177/09596836231211872 (DOI)001111087400001 ()2-s2.0-85178427803 (Scopus ID)
Forskningsfinansiär
Knut och Alice Wallenbergs Stiftelse, 2016.0083Vetenskapsrådet, 2014-05219
Anmärkning

Originally included in thesis in accepted form. 

Tillgänglig från: 2023-08-28 Skapad: 2023-08-28 Senast uppdaterad: 2024-04-26Bibliografiskt granskad
3. The influence of landscape setting on Holocene lake sediment composition in Swedish mountain lakes, determined with infrared spectroscopy
Öppna denna publikation i ny flik eller fönster >>The influence of landscape setting on Holocene lake sediment composition in Swedish mountain lakes, determined with infrared spectroscopy
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(Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
Nationell ämneskategori
Miljövetenskap
Identifikatorer
urn:nbn:se:umu:diva-213751 (URN)
Tillgänglig från: 2023-08-28 Skapad: 2023-08-28 Senast uppdaterad: 2023-08-28
4. Long-term development and trajectories of inferred lake-water organic carbon and pH in naturally acidic boreal lakes
Öppna denna publikation i ny flik eller fönster >>Long-term development and trajectories of inferred lake-water organic carbon and pH in naturally acidic boreal lakes
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2021 (Engelska)Ingår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 66, nr 6, s. 2408-2422Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Monitoring of surface waters in the boreal region over the last decades shows that waters are becoming browner. This timeframe may not, however, be sufficient to capture underlying trajectories and driving mechanisms of lake-water quality, important for prediction of future trajectories. Here we synthesize data from seven lakes in the Swedish boreal landscape, with contemporary lake-water total organic carbon (TOC) concentrations of 1.4–14.4 mg L−1, to conceptualize how natural and particularly human-driven processes at the landscape scale have regulated lake-water TOC levels over the Holocene. Sediment-inferred trends in TOC are supported by several proxies, including diatom-inferred pH. Before ~ 700 ce, all lakes were naturally acidic (pH 4.7–5.4) and the concentrations of inferred lake-water TOC were high (10–23 mg L−1). The introduction of traditional human land use from ~ 700 ce led to a decrease in lake-water TOC in all lakes (to 5–14 mg L−1), and in four poorly buffered lakes, also to an increase in pH by > 1 unit. During the 20th century, industrial acid deposition was superimposed on centuries of land use, which resulted in unprecedentedly low lake-water TOC in all lakes (3–11 mg L−1) and severely reduced pH in the four poorly buffered lakes. The other lakes resisted pH changes, likely due to close connections to peatlands. Our results indicate that an important part of the recent browning of boreal lakes is a recovery from human impacts. Furthermore, on a conceptual level we stress that contemporary environmental changes occur within the context of past, long-term disturbances.

Ort, förlag, år, upplaga, sidor
John Wiley & Sons, 2021
Nationell ämneskategori
Miljövetenskap Ekologi
Identifikatorer
urn:nbn:se:umu:diva-183358 (URN)10.1002/lno.11761 (DOI)000646653900001 ()2-s2.0-85104986862 (Scopus ID)
Forskningsfinansiär
Vetenskapsrådet, 2008-03741Vetenskapsrådet, 2011-03638Vetenskapsrådet, 2014-05219
Tillgänglig från: 2021-05-25 Skapad: 2021-05-25 Senast uppdaterad: 2023-08-28Bibliografiskt granskad

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